1. Field of the Invention
This invention relates to a hologram recording apparatus and method for producing a hologram for the purpose of instantaneously recognizing the minute vibration of an object and a change in the shape of the object, as well as patterns and characters, and for various other purposes as well. The invention further relates to an apparatus to which the above-mentioned apparatus and method are applied, an example of which is a unit for constructing an optical system necessary in laser applications technology, e.g., creation of holograms, recognition of object shape, recognition of character strings, interferometry experiments and diffraction experiments. More specifically, the unit is an apparatus for laying out and aligning the optical elements that construct the optical system. A method for this purpose is also provided.
2. Description of the Related Art
A so-called photographic plate and a photoconductor/thermoplastic hologram photographic plate are available as photosensitive photographic plates for holography. The former is obtained by coating a transparent supporting body (a glass substrate or the like) with silver halide photosensitive material used in photography. The latter is obtained by building up a transparent electrically conductive layer, a photoconductive layer which includes poly-N-vinylcarbazole and a thermoplastic resin layer on a transparent supporting body in the order mentioned.
A method of producing a hologram using a photographic plate involves irradiating a silver halide photosensitive material, which has been applied to the photographic plate, with reference light rays and light rays that have been reflected or transmitted by an object irradiated with laser light, and then developing the plate.
Though a high sensitivity is achieved with this method, the maximum diffraction efficiency is low (The larger the value of diffraction efficiency, the better the quality of the reproduced image obtained). In addition, it is necessary that the photographic plate be removed and developed in darkroom after exposure. The developing treatment is inconvenient as it requires the use of a troublesome process. Once the photographic plate has been removed for development, it is difficult to accurately return the hologram to its original position. As a result, real-time hologram interference cannot be achieved.
A hologram recording method (a method relying upon a thermoplastic) using a photoconductor/thermoplastic hologram photographic plate utilizes frost deformation of a thermoplastic resin. This method includes charging the thermoplastic resin, then softening the thermoplastic resin by high-frequency heating while irradiating the thermoplastic resin with reference light rays and light rays that have been reflected or transmitted by an object irradiated with laser light, and recording the interference fringes. This method has various advantages such as a high diffraction efficiency, spontaneity and reversibility.
However, it is difficult to control the optimum heating temperature and optimum heating time of the thermoplastic resin, and there are problems in terms of expansion and contraction of the substrate and deterioration of the resin layer due to repeated use. Moreover, this method requires a large high-frequency heating apparatus to thermally fuse the thermoplastic resin. It is difficult to reduce the size of the apparatus. Another drawback is that the problem of thermal strain, which influences the performance of the hologram, cannot be avoided.
On the other hand, in order to perform experiments regarding image formation by lenses and optical interference, and experiments and research regarding hologram creation, not only the light source but also such optical elements as lenses and beam splitters must be arranged and fixed along the necessary optical path. The optical system is susceptible to vibration, and even slight positional displacement of the optical elements can cause the optical path to become misaligned, in which case the optical elements must be realigned.
The conventional practice is to arrange the optical elements on an optical bench or isolation table adapted to resist vibration, and to assemble the optical system in two dimensions. Since the optical bench or isolation table is costly and heavy, the apparatus must be set up in a special laboratory, thus making it impossible to perform optical experiments in simple fashion.